Stress at work 'can increase breast cancer risk by a third'

Women who feel stressed at work could be at a dramatically increased risk of developing breast cancer, a study suggests.

It found women in demanding jobs are 30 per cent more likely to develop the disease than those who feel on top of their work.

The results of the study, which involved 36,000 women, appear to contradict previous research which has not found a link between stress and breast cancer.

More than 44,000 women are diagnosed with the disease every year and 12,000 die.

Although survival rates are improving, the number of women who develop breast cancer has also been growing for decades.

The increase has been blamed on a host of lifestyle and environmental factors, including rising obesity, increased alcohol consumption, not breast-feeding, and the tendency to have children later in life.

The latest findings, to be published next month in the journal Epidemiology, will focus attention on the role of stressful lifestyles.

It looked at data on 36,000 Swedish women aged 30 to 50 who were in work when the study started in 1990. The study followed the women until 2004, by which time 767 of them had been diagnosed with breast cancer.

The risk of breast cancer increased by around 30 per cent for women with stressful jobs after other factors, such as alcohol consumption, number of children, weight, and age, were taken into account. The Swedish researchers found no link between stress and cancer among women in part-time work.

The reason why stress might increase the risk is unclear, although studies show it may raise levels of the hormone oestrogen which can heighten the risk of cancer. Another theory is that stress changes women's behaviour, making them adopt unhealthy habits such as smoking and not exercising.

Lead researcher Dr Hannah Kuper, from the London School of Hygiene and Tropical Medicine, said stress could also potentially weaken the immune system.

Dr Kuper admitted it was difficult to explain the findings and the study had not attempted to measure other sources of stress, including those at home.

She also said the study only measured job stress at one point in the women's lives, which could have skewed the findings.

Recent research has found that long working hours and stress from work can bring on the menopause early and, in pregnant women, increase the risk of a miscarriage.

However, a Danish study of 7,000 women over 18 years found those with high levels of stress were less likely to develop breast cancer than women with low stress levels. Leading-cancer scientists yesterday said more research is needed before stress can join other well-known risk factors.

"One of the difficulties is that it is hard to measure stress, it's an objective thing. But if people are stressed, that can lead to unhealthy behaviour.

"If women feel stressed, they may not eat as well, they may drink more and they may do less exercise. All these can increase the risks of breast cancer."

Professor Amanda Ramirez, of Cancer Research UK, said: "Our work has shown no association between severely adverse life experiences and relapse of breast cancer. Our results suggest women with breast cancer need not fear that stressful experiences will precipitate the return of their disease."